They didn’t reveal in which model year the first AT&T-connected cars would ship. Nor did they say if such connectivity would come with all U.S. Nissans or only a subset of cars. So it’s difficult to say whether this deal is of the same significance as AT&T’s tie-up with General Motors. Starting with 2015 models, AT&T will replace Verizon as the telematics provider for GM’s OnStar, putting an LTE chip in every Chevy, Buick and Cadillac from that year forward.

How much Nissan uses of AT&T network will depend on how deeply it installs SiriusXM’s telematics services into its vehicles. Telematics cover a broad range of remote vehicle services that link the car to the internet and phone networks at large. Nissan and SiriusXM mention three features in particular: emergency assistance, stolen vehicle tracking and roadside assistance.

But most car makers telematics portfolios are growing to include features that connect your car directly to your smartphone even if the two are nowhere near one another. For instance, you can now use many automaker’s apps to unlock your doors, remotely start its engine and get a diagnostic report downloaded straight to your phone. And given that Sirius is in the driver’s seat here, infotainment services are sure to follow. (For more information see GigaOM’s connected car infographic.)

Many of those services will require two-way connectivity that SiriusXM can’t deliver alone. Its satellite networks have data channels can deliver traffic, weather and other information to the car, but there is no return path. AT&T’s GSM, HSPA+ and LTE networks would provide that critical car-to-internet connection.